Common practice in the medical field is the continuous measuring and analysis of carbon dioxide concentrations in exhaled breath of mechanically ventilated patients, anaesthetized patients, and patients suffering from particular forms of respiratory disease. Generally known as “Capnography”, in medical practice Capnography is typically used to obtain information about a patient's physiological condition and/or physical condition. Some examples of these applications may include: to evaluate patient's end-tidal carbon dioxide; to monitor severity of pulmonary disease; to corroborate that tracheal intubation and not esophageal intubation has been performed; to continuously monitor proper operation of ventilation equipment; and, to measure volume of carbon dioxide elimination to assess metabolic rate and/or alveolar ventilation. More information on Capnography may be found in “AARC Clinical Practice Guideline, Capnography/Capnometry during Mechanical Ventilation—2003 Revision and Update”, and Respiratory Care, May 2003, VOL 48, No. 5, all of which are hereby incorporated by reference.
Two methods are commonly used in the practice of Capnography, mainstream Capnography and side-stream Capnography. Both methods comprise the use of an appropriate breath sampler adapted to measure and analyze carbon dioxide samples in the patient's exhaled breath. The breath samplers generally employ technology based on, for example, infrared spectrography, molecular correlation spectrography, mass spectrography, Raman spectrography, or photo-acoustic spectrography, for the performance of the measurements and analyses.
In a mainstream Capnography system the breath sampler is directly coupled, through an appropriate adapter, to a patient airway tube connecting the patient to a ventilation machine. A sensor is inserted into the airway tube so that the exhaled breath passes directly over the sensor which measures the carbon dioxide concentration in the exhaled breath. The method is generally used with intubated patients as, for non-intubated patients, a mask is usually required which may be uncomfortable for patients in respiratory distress. In a side-stream Capnography system a breath sampler continuously draws samples of exhaled breath from the attached patient airway tube connecting the patient to the ventilation machine. Typically, a narrow diameter, flexible breath sampling tube extends from the breath sampler to the patient airway tube. Connection to the airway tube is typically by means of an airway adapter, which is a tube adapted to be connected to the patient airway tube (for example a tube exiting from a ventilator source) at one end, and through appropriate fittings, to the patient's intubation tube at the other end. Optionally, the airway adapter may be connected to a separate section of the patient airway tube at each end. Connection of the breath sampling tube to the airway adapter is usually performed through a sampling port in the airway adapter. The sampling port typically comprises a narrow bore tube, also referred to as “air collector”, perpendicularly extending at one end towards the central axis of the airway adapter tube. At the other end, the air collector generally extends outwardly through a wall of the airway adapter tube to connect, by means of appropriate sampling port connection fittings, to the breath sampling tube. The air collector may include one or more relatively short extensions, referred to hereinafter as “inlets”, generally perpendicularly extending from the air collector. The inlet comprises an aperture which is connected through a narrow bore to the bore of the air collector.
At the other end of the breath sampling tube is usually connected the breath sampler. The breath sampler is typically adapted with a pump which operates to continuously create a pressure drop along the path from the airway adapter to the breath sampler. By creating the pressure drop, which may also be referred to as “negative pressure differential”, exhaled breath samples are continuously drawn from the airway adapter through the aperture(s) into the sampling port and thereon through the breath sampling tube to the breath sampler. The accuracy in the measurement and analysis of the breath samples is dependent on the samples experiencing a continuous, smooth, laminar flow when traveling from the patient to the breath sampler, such that the carbon dioxide waveform arriving at the breath sampler is substantially the same as that in the patient airway tube.
Techniques are commonly utilized in side-stream Capnography systems to try to prevent liquids, which tend to accumulate in the patient airway tube, from entering the breath sampling tube. These liquids may include, for example, liquids related to patient secretions, such as for example, mucous, condensed-out liquids resulting from high humidity in the ventilation means, and medications and saline solutions provided to a patient during lavage, suction and nebulization procedures. Entry of the liquids into the breath sampling tube may cause partial or total blockage in the tube, interfering with the flow of the breath samples and affecting the carbon dioxide measurement and analysis. Furthermore, liquids entering the breath sampler may cause damage to the device.
Entry of liquids into the breath sampling tube is generally through the sampling port in the airway adapter. Typically, these liquids reach the sampling port as a result of any one or combination of the following conditions:    a) Directly during patient coughing.    b) During lavage procedures wherein liquids (generally a saline solution) are injected into the patient airway towards the lungs to break down thick secretions. These procedures are typically performed prior to suctioning and cleaning the patient airway tube and may result in the liquids reaching the airway adapter if not synchronized well with inhalation.    c) During movement of the patient airway tubing as a result of moving the patient or direct movement of the tubing itself. Liquids collecting along the patient airway tube may then flow into the airway adapter and consequently reach the sampling port.    d) When the airway adapter is the lowest point in the patient airway, liquids may collect at the bottom of the airway and, if not emptied periodically, they may reach the sampling port. Furthermore, when air or exhaled breath flow in their respective directions inside the patient airway tube during the inhalation/exhalation cycle, the liquids may splash across the apertures in the sampling port and enter into the sampling port.
Liquids reaching the sampling port are drawn in through the aperture in the inlet or air collector as a result of the pressure drop between the airway adapter and the sampling port. This condition may cause a blockage in the sampling port. Despite the blockage, generally the pump in the breath sampler continues to work for a period of time increasing the pressure drop between the point of the blockage and the breath sampler. The increase in the pressure drop typically results in the liquid being pulled into the sampling port and subsequently into the breath sampling tube. Eventually, the increasing pressure drop reaches a threshold value at which the pump is inactivated, but usually not before the liquid has caused a blockage in the sampling port and/or the breath sampling tube.
Numerous types of airway adapters and sampling ports used in the art are adapted with filtering systems for the prevention of liquids from entering the breath sampling line. Generally, there are drawbacks with such adapters and/or sampling ports as described below.
An airway adapter comprises a sampling port wherein the sampling port comprises a metal filter made of sintered metal powder. The liquids are blocked by the metal filter from entering into the sampling port and into the breath sampling tube. A problem with this sampling port is that the metal filter is quickly covered with liquids, requiring frequent replacement of the filter.
A different airway adapter comprises a hydrophobic baffle lining the interior circumference of the adapter along a portion of its length. An exit port extends from the baffle and connects to a breath sampling tube, the hydrophobic baffle permitting the passage of the breath samples. A disadvantage in this airway adapter is that the baffle quickly fills up with liquid interrupting the smooth flow of the breath samples, thereby requiring frequent replacement of the airway adapter.
Another airway adapter comprises a sampling port with multiple inlets extending from an air collector. The inlets are adapted to independently permit the breath samples to flow through without any substantial waveform distortion should an aperture be blocked in one of the inlets. Additionally, the blockage is not pulled into the air collector as the open inlet(s) prevents an increase in the pressure drop between the sampling port and the breath sampler due to the blockage. A drawback with this sampling port is that the blocking liquid has a tendency to migrate from one aperture to another as a result of air and exhaled breath flow in opposite directions during the inhalation/exhalation cycle. Furthermore, the proximity between the inlets, the reduced surface area between the inlets and the corners at the base of the inlets provide additional surface tension area for the liquids to attach to as they migrate. These conditions may contribute to blocking of all apertures and liquids entering the sampling port, requiring replacement of the airway adapter.
As discussed above, airway adapters and/or sampling ports known in the art are not generally well adapted to serve as a “first line of defense” against liquids found in a medical environment associated with the use of ventilation equipment. These adapters and/or sampling ports have a tendency to suffer from blockages which generally require their frequent replacement. Furthermore, in some cases, they are designed with filters which prevent liquids from flowing into the sampling port but at the expense of degradation in the waveform of the exhaled breath samples.
There is therefore a need for an airway adapter and/or sampling port capable of handling exposure to liquids generally encountered in medical environments associated with patient ventilation. The airway adapter and/or sampling port should be adapted to prevent the entry of liquids into the breath sampling tube without interfering with or substantially altering the waveform of exhaled breath samples.